Visual mental imagery is used in memory, reasoning, and learning. A deeper understanding of the nature of imagery has practical implications for the diagnosis and treatment of a variety of neuropsychological conditions. The general goal of this research is to conduct functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) studies to investigate the representations and processes that underlie visual mental imagery. FMRI will be used to identify the neural structures that underlie different aspects of visual imagery, and TMS will be used to investigate the causal role of specific activated areas in task performance. The specific goals are to perform six studies addressing the following issues: (1) Do differences in the orientation of imaged objects map directly onto differences in the pattern of activation in Area V1, and is the pattern of activation sufficient to identify the orientation at which an image was formed? (2) Is V1 more likely to be activated when participants must use high resolution to examine details of imaged objects? (3) Is V1 activated during tasks that require visualizing shape but not during tasks that rely on visualizing locations or spatial relations? (4) The mechanisms underlying image maintenance over time have received virtually no attention in the literature. We directly compare the mechanisms involved in generating an image and maintaining it over time, and examine the effects of stimulus complexity on the two functions. (5) We also study how images of locations or spatial relations are maintained, and we compare the processes underlying such image maintenance with those underlying "spatial working memory." (6) Finally, we directly compare the brain areas that are activated during imagery for shapes, imagery for locations, and image rotation. Mental rotation is often considered a "spatial task," but we hypothesize that it also draws on mechanisms that specify shape. We not only compare these tasks with respect to a baseline, but also compare the brain areas in which variations in activation predict variations in performance on each task.